1. Field of the Invention:
The present invention relates to a gel permeation chromatograph for analyzing a sample.
2. Description of the Prior Art
FIG. 1 shows a conventional gel permeation chromatograph system wherein a solvent tank (1), a line filter (2), a constant flow feeding pump (3) and a distribution block (4) are connected in series and it is divided at the distribution block into a sample side passage comprising a sample injector (5) and a sample analysis column (6) and a reference side passage comprising a reference side column and the other ends of these columns are connected to a detector (8).
The gel permeation chromatograph system for dividing a solvent fed from one constant flow feeding pump (3) into two passages has been used. There has been no trouble for a low speed gel permeation chromatograph which usually requires about 4 hours for the measurement of one sample. However, a high speed gel permeation chromatograph system which requires only about 20 to 40 minutes for its measurement has been commerciallized depending upon a development of a gel permeation chromatograph carrier having high number of theoretical plates.
In the column having high number of theoretical plates, it is usual to fill in high density, high functional gel which has a particle size of 1/6 to 1/10 times of the particle size of the gel for the low speed gel permeation chromatograph system as the gel in the column.
In the case of the conventional gel permeation chromatograph system having the structure shown in FIG. 1 is used for measuring by such column filling the gel in high density, when a sample is fed into the analysis column (6) in a measurement of the sample having large molecular weight and wide molecular weight distribution, an inner pressure in the analysis column (6) is elevated by its viscosity effect (about 2 Kg/cm.sup.2 in a case of injecting 2 ml of 0.3% of polyethylene having a molecular weight of several hundred thousand at 135.degree. C.) whereby the solvent fed from the constant flow feeding pump (3) is distributed depending upon a ratio of the inner pressure of the analysis column (6) to that of the reference side column (7) and a large ratio of the solvent is fed to the reference side column (7) depending upon the ratio of the different inner pressures.
This phenomenon is remarkably found when the sample reaches to a column end filter at the inlet of the column and it passes through the filter. During the time passing the column after the column end filter, the sample is expanded in the column to reduce gradually the inner pressure. Accordingly, a quantative accuracy and a reproducibility of the chromatogram are decreased and a fluctuation of a base line and a shock at the injection of the sample are increased.
FIG. 2(A) shows a chromatogram of a polyethylene having a molecular weight of several hundred thousand in o-dichlorobenzene as a solvent by two columns connected in series at 135.degree. C. The variations of the base line are found (a) at the time of the injection of the sample or (b) at about initiation of an elution to a discharge limit for the first column in a serial connections of plural columns. Moreover, the inner pressure of the column is gradually changed to cause (c) a step of the base line or a drift.
FIG. 2(B) shows a chromatogram under the variation of the inner pressure of the column from the initiation to the elution.
Such phenomena are remarkable when a differential refractometric densitometer having higher flow rate dependency that that of the other detector, is used as a detector for a gel permeation chromatograph system at a measurement of a gel permeation chromatogram at high temperature in which a flow rate balance highly affects to a stability of the base line.